The present invention relates to sewing machines in general, and more particularly to a method of and arrangement for operating a sewing machine, especially a multi-needle sewing machine, in which the material being sewn is advanced in any arbitrary direction along a sewing plane.
In sewing machines, it is encountered time and again that the needle is slightly deviated from its initial course or bent during its penetration into the material being sewn when the material is advanced in any direction along the sewing plane during the time that the needle passes into and/or beyond such material. This deviation or bending of the needle depends on the extent of advancement of the material while the needle is in engagement with such material, on the stability of the needle, and finally on the properties of the material being sewn, that is especially on how strong or how yieldable this material is.
In the classic sewing machine, which is equipped with a transporting arrangement for the material being sewn, the extent of deviation or bending of the needle is negligibly small, inasmuch as the transporting arrangement, generally speaking, advances the material being sewn only during such time periods during which the needle is situated outside the material being sewn.
Furthermore, there are known sewing machines in which the needle performs a defined movement together with the material being sewn. These machines are known as so-called needle-transport sewing machines. However, such machines permit the advancement of the material being sewn only in one direction, that is, in the direction which extends parallel to the plane in which the gripper is angularly displaced. There are also already known sewing machines in which not only the needle but also the gripper perform defined movements, which are derived from one or more cam discs. Such machines are commonly known as zig-zag or ornamental stitch sewing machines. Even in these sewing machines, however, the material being sewn is advanced only in the direction which extends parallel to the plane in which the gripper is angularly displaced or pivoted.
Newer developments in the field of automatization even in the area of sewing machines have led, especially in large sewing machine arrangements, such as multi-needle machines, to a situation where the material being sewn is advanced in any and all directions along a sewing plane in correspondence to the action of mechanical control cam curves and electronic control commands, in an automated manner. In this manner, there can be provided arbitrarily selected sewing patterns, such as inclined diamond or diamond pattern, or circular arc or circular pattern, or even contours of arbitrary shapes. In the machines of this kind, it is often no longer possible, especially in such sewing machines that operate at high speeds, so to control the advancement of the material being sewn that such advancement only takes place when the needle is not in contact with the material being sewn. The result of this is often a deflection of bending of the needle in the direction in which the material being sewn is being advanced.
This deflection or bending of the needle is relatively harmless, so long as the material being sewn is being advanced parallel to the displacement plane in which the gripper is being turned or pivoted. However, it becomes problematical when the material being sewn is being guided or advanced transversely to this gripper displacement plane, that is, either normal to the gripper displacement plane or at an angle smaller than 90.degree. with respect to the latter, with a corresponding movement component normal to this displacement plane. As a result of this, there occurs also the deflection or bending of the needle transversely with respect to the gripper displacement plane. When this deflection or bending of the needle takes place away from the gripper, so that the distance between the needle and the gripper becomes larger than normal, there exists the danger that the tread loop may no longer be engaged or caught by the gripper tip. This results in faulty stitches and in thread breakages. When, on the other hand, the deflection of bending of the needle occurs in direction toward the gripper, it may happen that the gripper tips and the needle tip meet or collide. The result then may be breakage of the needle or damage to the gripper tip.
It is true that it was attempted to keep these disadvantageous consequences within limits by making the stitching hole which is provided in a support plate for the material being sewn and through which the needle passes on its way beyond the material and toward the gripper region, relatively narrow based on the desire better to guide the needle. However, from this results, in turn, another disadvantage, namely, that an increased wear of the needle is encountered owing to the lateral friction of the needle against the surface bounding this hole. Furthermore, an additional drawback is that the needle is sharpened during the up-and-down movement of the needle into, through, and out of the stitching hole, so that the needle becomes unusable for sewing after only a relatively short period of use thereof.
A further attempt at reducing the deflection or bending of the needle in accordance with conventional approaches resided in enlarging the cross section of the needle. However, this approach results, especially when the material being sewn is sensitive, in relatively large piercing holes with less than esthetically pleasing appearance, and very often in the damage to or breaking of the threads of the woven or knitted material being sewn.